In order to produce various flat prints or printed packing materials, such as paper boxes or thermoplastic films, it is necessary for flat prints or films to be cut along a designed cutting line, and for box-shaped packing materials to be cut along a designed cutting line of a printed paper board prior to forming the board into a box.
Such a cutting process for producing flat prints, paper boxes, or thermoplastic films has to be performed using a single-edged cutting blade which extends along a desired cutting line. Such a cutting blade is set on a flat wood block in a way such that the blade has a uniform height. In such a case, the sharpened surface of the single edge of the blade faces outward. The wood block, with the cutting blade, is installed on a press, which is used for cutting such flat prints or packing materials.
Typical cutting blades are produced by cutting a thin special steel strip into pieces. Such a steel strip has a band-shaped configuration and is sharpened at one edge prior to being subjected to the bending and cutting processes. Such a metal strip has to be bent and cut into cutting blades which individually form a designed cutting line along which flat prints or packing materials are cut by the cutting blade. After the metal strip is bent and cut into cutting blades, one or more cutting blades are set on a wood block. Therefore, it is primarily necessary to precisely bend and cut the metal strip into cutting blades. In addition, the metal strip is also processed through a plurality of sub-processes as follows.
For example, the metal strip has to be regularly notched at the lower edge opposite to the sharpened edge, thus forming bridge notches at the lower edge. Such bridge notches are for firmly holding the position of a cutting blade when the blade is set on a wood block. That is, the bridge notches almost completely prevent the set position of the cutting blade on the wood block from being unexpectedly deformed due to external impact. Sometimes, it is necessary to form a plurality of V-notches along the sharpened edge of the metal strip, thus form a cutting blade which is preferably used for forming perforated lines on prints, such as stamps. Sometimes, the metal strip may be bent at right angles. In such a case, a bending slot has to be transversely formed on a side surface of the metal strip prior to bending the metal strip at right angles. When the metal strip has to be precisely bent, it is preferable to bend the metal strip manually rather than mechanically and this forces the metal strip to be subjected to a marking process of forming bending points on the metal strip prior to manually bending the metal strip.
Of course, the above-mentioned sub-processes of forming bridge notches, V-notches, bending slots and bending points are well known to those skilled in the art. However, in known blade forming devices, such processes are not performed through integrated work, but are separately and selectively performed, so that the known devices fail to achieve desired precision and reduce productivity, and increase the production cost of the cutting blades.
In the known devices, the process of cutting the metal strip into desired cutting blades is separately performed from the above sub-processes, thus more reducing productivity and increasing the production cost of the cutting blades.
In an effort to overcome such problems, a long metal strip, with a sharpened edge, may be wound around a feeding roll so as to be forcibly and continuously fed from the roll to a bending nozzle. At a position around the bending nozzle, the metal strip comes into contact with a plurality of bending pins which are used for bending the metal strip into a desired configuration.
As well known to those skilled in the art, such a bending process, using a bending pin, is numerically controlled by a computer. That is, a plurality of bending pins are positioned around the bending nozzle and are precisely rotated in opposite directions in response to control signals output from the computer, thus bending the metal strip coming out from the bending nozzle. Such a bending process may be referred to, for example, in Japanese Patent Laid-open Publication No. Heisei. 8-99,123.
In the typical blade forming devices, the metal strip may be cut into a plurality of pieces, having designed lengths, before the metal strip reaches the bending nozzle. In a brief description, the metal strip may be cut into pieces before a bending process. Alternatively, the metal strip may be cut into pieces after a bending process as disclosed in Japanese Patent Laid-open Publication No. Heisei. 8-243,834. In this Japanese Patent, the metal strip, coming out from the bending nozzle, is repeatedly bent in opposite directions until the metal strip is cut due to fatigue fracture.
However, the typical blade forming devices are problematic in that they fail to produce high quality cutting blades and cannot produce the cutting blades through integrated work.
That is, the configuration of the bridge cutting jig, installed in the typical devices, is fixed, so that it is almost impossible to change the intervals or configuration of the bridge notches of the metal strip. In addition, the typical devices have to separately perform a machining process of forming such bridge notches on the metal strip, so that the devices reduce productivity and increase the production cost of the cutting blades.
Another problem of the typical blade forming devices is caused by the bending pins used for bending the metal strip into a desired configuration. That is, the bending pins have to be held by a complex holding means, thus complicating the construction of the cutting blade forming device. In addition, it is almost impossible to precisely adjust the bending angle of the bending pins without causing error.
When the metal strip is subjected to a bending process after a cutting process, the cutting blades have accumulative error during the bending process, so that the cutting blades have a low precision.
In addition, when at least one of the bending pins is frictionally abraded, it is almost impossible to precisely center the bending pins. In such a case, the bending pins have to be repositioned one by one and this reduces work efficiency while bending the metal strip.
During a bending process using the typical device, the sharpened edge of the metal strip comes into contact with the bending pins, so that the sharpened edge may be damaged.
The most important problem, experienced in the typical blade forming devices, is caused during a cutting process. That is, since the metal strip from a bending process is cut into pieces by repeatedly bending the metal strip in opposite directions until the metal strip is cut due to fatigue fracture, the edge, along which the metal strip is cut, is not smooth, but is exceedingly rough with burrs, thus spoiling the appearance of the cutting blades. In order to remove such burrs from the cutting blades, the blades have to be subjected to an additional grinding process. In addition, after the metal strip is cut into pieces, it is necessary to finally machine the pieces so as to produce resulting blades and this forces the metal strip to be cut into pieces with machining allowance. Due to such machining allowance, it is almost impossible to produce high precision blades.
Therefore, it is preferable to perform the processes of forming the bridge notches on a metal strip, bending the metal strip into a designed configuration and cutting the metal strip into cutting blades through integrated work while precisely adjusting the bending angle of the bending pins and finely cutting the metal strip into cutting blades. In such a case, the. cutting blades from the cutting process may be free from any additional machining process.
In addition, it is necessary for the blade forming devices to be flexibly used for processing metal strips having different sizes. The blade forming devices also have to be designed for effectively bending the metal strips into different configurations when necessary.